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Cummins 903 Turbo Replacement
The levels of smoke on my coach had been increasing for a while. Someone suggested I check the turbo for failed oil seals. The exhaust side showed no signs of oil. I removed the turbo to intake hose and found a lot of oil. 

The original turbo was a ST50, a design that was fairly antiquated when it was released. A rebuild kit is available, I thought an upgrade was the better route. There are a few options and I went with a Borg Warner BHT3B. This is a non-pulse manifold turbo and a direct fit. I only needed to change the oil feed fitting on the turbo.

While the turbo was off I pulled the injector pump and replaced the seals, gaskets and o-rings using an aftermarket rebuild kit and some Cummins seals. The kit worked fine but I would go directly to Cummins next time, the parts are readily available and may be of better quality.  I was careful to not change any of the calibration settings. The pump was in pretty good shape, however the AFC diaphragm had failed and I suspect it prevented the AFC from operating properly.

The last piece of this project was a new muffler. I went with the setup Richard posted and completely agree with his review. The muffler seems very well made, straight through design, and barely if any louder than the old Riker.

Search: Alternate Muffler Replacement

I now have about 600 miles of road testing, and its better than I expected. Once warmed up it produces no smoke, turbo spools faster and much higher, and better fuel rail pressure. The old turbo would slowly produce 8psi under heavy load and maybe 2psi on level ground. The new turbo produces 15psi under heavy load and 6psi on level, and spoils quickly. I am not sure what the change was in fuel pressure but I now run about 60 psi on level ground and up to 145psi (i think it topped about 125psi before) under heavy load.

1983 Newell
Cummins VT903
Allison 654CR
Nicely done.
I had a 903 in my coach, same turbo problem, a replacement ST50 made it better but I developed injector leakage and needed valve work.
I decided to modernize and swap it with a takeout 8.3 and 6 speed Allison.
If you get to needing a major overhaul, an 8.3 with a side radiator is a good option; same hp, more torque, and better mpg.
My 903 went to a tractor puller in PA, he converted it to methanol and pumped 2000hp from it.

1983 38' Classic #007
8.3 Cummins, Allison 6 spd.
"Any other Way"

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